Headrests installed on the seat back rests of vehicles have usually two parallel spaced rods of the headrest, which are accommodated in sleeve arrangements for the headrest, which are fixed on the frame of the back rest. The headrest rods are often bent in a U-shape. The bridge of the U-shaped portion is located inside of the headrest. Known sleeve devices for headrests are comprised of a sleeve body to be inserted into an opening in a frame of a vehicle seat. The sleeve body includes an inner axial passage to accommodate a rod of the headrest and an external side provided with fixing means to fix the sleeve body in the opening of the frame. The inner axial passage comprises an inner wall, a top end portion and a bottom end portion. A head portion with internal locking means to fix de rod of the headrest in at least one axial position in the sleeve body is provided. The head portion is equipped with a locking means, which co-operates with grooves such as a toothing or the like in the rod of the headrest, so that it is possible to arrest the headrest at a predetermined height or to change the desired height of the headrest, respectively. Further, it is known to make the head portion and the sleeve body portion into a one-piece sleeve body made of plastic material. A sleeve device of this kind is disclosed for example in EP-0875471-A1.
The sleeve body is fixed in a frame of the back rest of the seat, and it is thus subject to tolerances. The sleeve device and the U-shaped rods are also subject to tolerances when it is manufactured. The distance between the rods for the headrest is not always exactly the same, so that, when said distance does not correspond to the distance between the axes of the installed sleeve devices, the rods have to be bent somewhat, either away from each other or towards each other. However, by doing so they are no more exactly parallel. In addition to the problems associated to the distance between rods, noise problems are also originated due to the presence of gaps between the external diameter of the metal rods and the diameter of the holes, lack or parallelism between holes or the tubes of the frames. A solution to these problems, would be to design the sleeve and rod to fit tightly with each other to avoid any gap in between, however in that case, the metal rods would not slide smoothly along the sleeves. Therefore, it is desirable to obtain a good balance between noise problems known as BSR (Buss Squeak Rattle) and a nice feeling in the movement of the headrest with a reasonable sliding effort for the user.
In order to compensate the individual tolerances, the accommodation of the rod of a headrest in a sleeve device has to admit variances. However, these variances entail the possibility of generating noise in the sleeve devices during driving by a vibration of the headrest or of the rods of the headrest, respectively, which is unpleasant for the user of the seat, particularly as it is generated in the region of the ears of the user. In this context, it has already become known to pre-stress the headrest rods inside the sleeve body by springs, in order to regulate the sliding movement of the rod within the axial inner passage of the sleeve body and to dampen the said noise. However, with these known means, damping of the noise can only be achieved in an insufficient manner.
To provide enhanced damping, sleeve devices comprising bushings or rings of flexible material antifriction material to engage the sleeve body to the frame or to guide the rod in the axial inner passage of the sleeve body have designed, so that transmission of vibrations from the frame to the rod of the headrest and generation of noise is reduced.
FR-2917681-A1 discloses a sleeve device for headrests comprising a spacing dispersion adjustment device with elastomeric elements placed, between the frame and the sleeve body at both sides of the sleeve body. The structure of this sleeve device is rather complex and, moreover, no noise-dampening is provided between the rod and the sleeve body.
JP-1089665 discloses a sleeve device where elastomeric elements are positioned between the head and the sleeve body so as to dampen the transmission of vibrations from the frame to the headrest.
EP-1609665-A2 discloses a sleeve device for a headrest with tolerance compensation, comprising a sleeve body of plastic material for the accommodation of a rod of the neck rest, the sleeve body including at least one integrally formed resilient portion which is biased towards the interior of a sleeve body against an accommodated rod, where a wire portion is attached to the outer side of the sleeve body parallel to the axis of the sleeve body such that the wire portion can be resiliently deflected away from the sleeve body, the wire portion engaging the outer side of the resilient portion. In this sleeve device, dampening of the transmission of vibrations from the sleeve body to the rod of the headrest is rather poor. Moreover, the structure is rather complex and relatively difficult to manufacture.
FR-2936749-A1 discloses a sleeve device with a sleeve body for slidably receiving a rod of a headrest which includes a plastic sheath, and which has an inner transversal dimension larger than a transversal dimension of the rod to permit the rod to slide between upper and lower positions. A free end part of the rod extends outside an inner tubular envelope, such that a lower part of the sleeve presents a clearance with the rod in a lower position of a head-rest assembling frame and is transversally supported against the rod in an upper position of the frame. The sheet body comprises an upper portion of a hard plastic material, and a lower portion made of a resilient elastomeric material that avoids transmissions of vibrations from the frame to the rod of the headrest and to adapt itself to deviations of the rods when inserted into the sleeve body. This structure provides a rather poor guidance of the rod within the resilient lower portion of the sleeve body, and is moreover complex to manufacture.
EP-1652723-A2 discloses a sleeve device for a headrest, comprising a sleeve body adapted to be inserted into an opening in a frame of a vehicle seat, the sleeve body having a through going axial passage adapted to accommodate a rod of the neck rest, and the sleeve body having further a head portion which includes internal locking means to fix the axial position of the rod in the sleeve body and a shank portion joining the head portion, the sleeve body having an external side which includes means to fix the sleeve body in the opening of the frame, wherein in upper and lower end portions the passage has radially annular enlargements, and a preferably radially expandable sliding bushing of anti-frictional plastic material is accommodated by the enlargements which encircle the rod, and an elastomeric material is accommodated in the intermediate space between the sliding bushing and a wall of the passage. The bushings are made of a hard material whilst the elastomeric material is an elastomeric plastic foam, preferably PUR-foam. Whilst the dampening effect achieved by this structure is acceptable, manufacturing the sleeve device is rather complex as it requires insertion of each of the bushings followed by injection of the elastomeric material into the intermediate space between the sliding bushing and a wall of the passage.